Add weighting to calculation for keeping battery longer as emergency reserve

[peter1rhodes]

The problem

I don't believe this functionality currently exists, but I would find it useful. Currently, I have plenty of solar to see me through every day, so my battery charges overnight on the cheap rate and discharges during the day. Often, however, the battery discharges in the morning and stays down near the Best Keep SoC for most of the day. This is fine, but for preference, I would prefer to discharge later in the day, just to reduce the time window with less charge kept aside, as in the event of a powercut, I'm 'exposed' to risk for longer this way. In terms of export rates, it makes no difference, so predbat picks a time of day either at random or based on grid CO2 intensity if I put a carbon weighting in.

My suggestion

Incorporate an optional weighting, call it k (default 0), which rewards solutions per kWh that is held for an hour, as a reward. Thus, solutions which keep a 15kWh battery full all day before exporting down to 5kWh, when compared to a solution which discharges down to 5kWh 12 hours earlier, will show up as 12h x 10kWh x k = 120 k pence better. So a value of k = 1p/kWh.h will make this solution 120p better.